1. Field of the Invention
Aspects of the present invention relate to a flat panel display device and a method of manufacturing the same, and more particularly, to a flat panel display device with uniform light emission characteristics and a method of manufacturing the flat panel display device.
2. Description of the Related Art
Since the brightness of flat panel display devices, e.g., organic light emitting display devices, is determined by the amount of current flowing through the flat panel display devices, the flat panel display devices are driven by converting an input voltage signal into an output current. In this regard, the electron mobility of a thin film transistor of a pixel circuit is very important.
Monocrystalline silicon wafers may be the best choice considering only the electron mobility and uniformity of thin film transistors. However, since such monocrystalline silicon wafers are expensive, thin film transistors for flat panel display devices are formed of polycrystalline silicon that is prepared by depositing and crystallizing amorphous silicon on a glass substrate.
However, since such a glass substrate is fragile and deforms at a temperature higher than 400° C., a method of forming a polycrystalline silicon thin film in which a glass substrate rarely deforms during crystallization is desired.
For example, a polycrystalline silicon thin film may be selectively formed to a thickness of approximately 500 Å by excimer laser annealing (ELA). It is known that ELA ensures the highest degree of crystallization and uniformity among existing low temperature annealing processes, and particularly when being applied to an active matrix organic light emitting display device, ELA produces a flat panel display device having the highest image quality among the existing low temperature annealing processes.
However, ELA is expensive when applied to large panels with a size of 30 inches or more, and ELA has a maximum excimer laser width of approximately 470 mm. That is, a panel cannot be entirely scanned for crystallization by ELA at one time because the excimer laser width is narrow, and thus the panel is scanned several times, thereby producing overlapped areas in which excimer laser beams overlap.
The overlapped areas in which the excimer laser beams overlap produce crystallized polycrystalline silicon having less uniform characteristics than other areas in which the excimer laser beams do not overlap. If a pixel circuit is formed in the overlapped areas, image quality is degraded. For example, the brightness of a corresponding pixel is reduced or lines may appear on a screen.